What kind of terrain is suitable for damming and siltation (the title is an isometric map, and the isometric height of land A)?

In the contour map, choose a small ditch and a small river with low terrain, choose a narrow part, and take soil from the mountains with high terrain on both sides to build a dam with the same height as the mountains, and lock the whole ditch, and then let the flood water silt up in the ditch until the whole ditch is silted up into a small plain or a small basin. The gully should be chosen to have a narrow portion that is easy to build a dam. Hope to help you!